USMLE Step 3 Practice Question: Beta-Blockers Video Explanation

Gearing up for your USMLE Step 3 Exam? With an exam riddled with long, complicated questions and a short timer, practice is going to be your best bet on preparing for this exam. One question from our USMLE Step 3 practice question bank has been particularly tricky for our users, so we’ve asked Dr. Roger Seheult from MedCram to take a stab. Check out his video explaining how to determine the number of patients needed to treat to save 1 life with the addition of beta-blockers.

The Question:

BACKGROUND: Beta-blockers reduce mortality in patients with chronic heart failure or systolic dysfunction and who are on background treatment with diuretics and angiotensin-converting enzyme inhibitors. This study seeks to determine whether or not carvedilol reduces risk of mortality compared to standard treatment with diuretics and ACEI.
METHODS: In a multicenter, double-blind, and randomized parallel group trial, we assigned 1511 patients with chronic heart failure to treatment with carvedilol (target dose 25mg 2x daily) plus ACEI and diuretic therapy and 1518 to standard treatment with a combination of ACEI and diuretic. Patients were required to have chronic heart failure (NYHA II-IV), previous admission for a cardiovascular reason, and an ejection fraction of <0.35. All patients also had been treated optimally with diuretics and angiotensin-converting enzyme inhibitors unless not tolerated. Primary endpoints were all-cause mortality and the composite endpoint of all-cause mortality or all-cause admission. Analysis was conducted by intention to treat.
FINDINGS: Mean study duration was 58 months (SD 6). Mean ejection fraction was 0.26 (0.07), and mean age was 62 years (11). All-cause mortality was 34% (512 of 1511) for carvedilol and 40% (600 of 1518) for the control group (hazard ratio 0.83 [95% CI: 0.74-0.93], p=0.0017). Reduction of all-cause mortality was consistent across predefined subgroups. Incidence of side effects and drug withdrawals did not differ substantially between the 2 study groups.

Which of the following represents the number of patients needed to treat to save 1 life with addition of beta-blockers?

A. 1 / (0.40 – 0.34) (Correct)
B. 1 / (0.34 – 0.40)
C. 1 / (40 – 34)
D. 1 / (34 – 40)
E. 1 / 0.83


EXPLANATIONS: A. TRUE: The number needed to treat (NNT) is a statistical calculation that identifies the number of patients that must be treated with the trial intervention to save 1 life. The calculation is as follows: NNT = 1 / (% risk in control group) – (% risk in treatment group).
B. FALSE: This calculation reverses the control and treatment group numbers.

C and D. FALSE: These calculations inadvertently utilize the integral numbers (not percentages) for calculating risk in both study arms. E. FALSE: This calculation is the inverse of the hazard ratio, which is unrelated to the NNT.

Reference: 1. Le T, Bhushan V, Skelley N. First Aid for the USMLE Step 2CK, 8th ed. New York, NY: McGraw-Hill. 2012. 2. Poole-Wilson PA, et al. Comparison of carvedilol and metoprolol on clinical outcomes in patients with chronic heart failure in the Carvedilol Or Metoprolol European Trial (COMET): randomised controlled trial. Lancet. 2003 Jul 5;362(9377):7-13.

USMLE Step 3

The USMLE Step 3 exam is the third and final part of the USMLE exams. By now, you’ve learned and mastered a lot of the materials you need to ace this exam, which can be proven by its 96% pass rate. The one part of this exam that is notoriously discussed as a pitfall, is timing. The best way to combat short time and complicated questions, is practicing your test taking skills. Using practice questions that are designed to mirror those found on the actual exam are a great way to prepare yourself.

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